1. Field of the Invention
The present invention relates to a portable digital broadcasting reception apparatus adopting digital broadcasting reception and telephone functions, and more particularly, to a telephone signal cancellation circuit, a digital broadcasting reception circuit and a portable digital broadcasting reception apparatus for preventing reception sensitivity from being degraded due to a high powered telephone signal by blocking inflow of an interference noise signal, that is, the telephone signal such as a Global System for Mobile Communication (GSM) telephone and a mobile telephone signal, when the digital broadcasting such as a digital video broadcasting handheld (DVB-H) is received, for improving reception performance and productivity of digital broadcasting, and for increasing a DVB-H maximum reception frequency band limited by the interference noise signal up to 860 MHz.
2. Description of the Related Art
Recently, as digital-broadcasting has been receiving attention, various researches have been in progress for developing a Digital Multimedia Broadcasting (DMB) technology in Korea and some countries, and for developing a digital video broadcasting (DVB) technology in Europe.
The DVB is a shortened word of Digital Video Broadcasting and includes a digital video broadcasting terrestrial (DVB-T) for receiving broadcasting from a broadcasting station at a fixed device of home or office and a digital video broadcasting handheld (DVB-H) considering low power, mobility and portability of a mobile phone or a portable video device.
As the mobile terminal is multiplexed, a mobile phone having the DVB-H is about to be launched. When one terminal supports at least two functions such as Global System for Mobile Communication (GSM)/general packet radio service (GPRS) and the DVB-H, proper response against reception sensitivity deterioration of each module by a mutual interference affect is required.
Also, the entire original DVB-H reception bandwidth ranging about 470 MHz to 860 MHz cannot be used due to the interference noise signal. That is, the DVB-H reception bandwidth is limited to about 470 MHz to 750 MHz, which corresponds to a partial frequency band of the entire reception bandwidth of DVB-H.
FIG. 1 is a conventional DVB-H GSM mobile phone.
Referring to FIG. 1, the conventional DVB-H GSM mobile phone includes a GSM communicating unit 11 for transmitting/receiving a GSM signal of about 900 MHz where TX ranges 880 MHz to 915 MHz and RX ranges 925 MHz to 960 MHz, a DVB-H receiving unit 12 for receiving a DVB-H broadcasting signal having a band ranging about 470 MHz to 750 MHz, and a main control unit 13 for controlling a transmitting/receiving operation of the GSM communicating unit 11 and a receiving operation of the DVB-H receiving unit 12.
A DVB-H broadcasting frequency band and a GSM-TX frequency of the conventional DVB-H GSM mobile phone is described with reference to FIG. 2.
FIG. 2 shows a spectrum of the DVB-H broadcasting frequency band, the GSM-TX frequency band and a basic DVB-H broadcasting frequency band of the conventional DVB-H GSM mobile phone. The frequency band of the DVB-H broadcasting ranges about 470 MHz to 750 MHz and the GSM-TX frequency band ranges about 880 MHz to 915 MHz. The basic DVB-H broadcasting frequency band required for a typical DVB-H system ranges about 750 MHz to 860 MHz.
In the conventional DVB-H GSM mobile phone, a situation that a GSM telephone call is performed through the GSM communicating unit 11 for receiving digital broadcasting through the DVB-H receiving unit 12 may be generated. Also, a situation that a telephone call is performed through a GSM communicating unit of other DVB-H GSM mobile phone in a close distance while receiving digital broadcasting through the DVB-H receiving unit 12.
The GSM communicating unit 11 amplifies power of a GSM-TX signal into high power of about +33 dBm through an internal power amplifier. Accordingly, when the GSM-TX signal of the high power come to the DVB-H receiving unit 12, the GSM-TX signal operates for the reception signal of the DVB-H broadcasting as noise and an input end of the DVB-H receiving unit 12 includes a band-pass filter (BPF).
However, when a band ranging about 470 MHz from 860 MHz, i.e., a basic DVB-H reception bandwidth, is set up as a pass band based on the band-pass filter, a GSM-TX signal cannot be attenuated enough. Accordingly, the DVB-H reception band ranging 750 MHz to 860 MHz cannot be used and only the reception band ranging 470 MHz to 750 MHz of the conventional DVB-H reception apparatus is limitedly used.
The band-pass filter passes the frequency band of the digital broadcasting ranging about 470 MHz to 750 MHz, includes the GSM-TX frequency band and blocks the frequency band larger than about 800 MHz.
Although the band-pass filter included in the DVB-H receiving unit 12 of the conventional DVB-H GSM mobile phone blocks the GSM-TX signal, attenuation of the GSM-TX signal by the band-pass filter is not enough. Therefore, there is a problem that the GSM-TX signal flows to the DVB-H receiving unit 12 as noise and deteriorates the reception sensitivity of the DVB-H broadcasting.
A characteristic that the GSM-TX frequency band is attenuated by the conventional band-pass filter will be described with reference to FIG. 3.
FIG. 3 is a graph showing the frequency characteristics of the conventional reception apparatus of FIG. 1.
m1 shows that an attenuation rate with respect to 880 MHz in the GSM-TX frequency band is about −41.009 and m2 shows that an attenuation rate with respect to a frequency component of 915 MHz in the GSM-TX frequency band is about −42.428 dB.
Although attenuation performance of larger than −45 dB with respect to the GSM-TX frequency band is required to satisfy a specification of the DVB-H reception apparatus, there is a problem that the conventional DVB-H GSM mobile phone using the band-pass filter does not satisfy the specification of the DVB-H reception apparatus.
Also, if the bandwidth of the band-pass filter is designed in a range of 470 MHz to 860 MHz to acquire the conventional DVB-H reception band, the attenuation performance for the GSM-TX frequency band is further deteriorated, disadvantageously.